In the field of optical and electrical switching, the prior art recognized the use of organic thin films as switching media. Impedance changes which accompany this switching are known to be associated with molecular motion due to Joule heating which results in either crystallization phase transitions, metal filament formation, or elimination of compositional disorder. Switching has also been related to electrical breakdown of the organic thin film due to weak spots in the switching material.
Switching by means of electrochemical changes in the switching media has also been disclosed. By way of illustration, switching due to electrochemical changes in a charge transfer salt, e.g., a metal complexed with tetracyanoquinodimethane (TCNQ), tetracyanonaphthoquinodimethane (TNAP), tetracyanoethylene (TCNE), dichlorodicyanobenzoquinone (DDQ), or TCNQ derivatives is disclosed in U.S. Pat. Nos. 4,574,336; 4,507,672; and 4,371,883, the disclosures of each of these three patents being incorporated herein by reference. The TCNQ and TCNQ derivative materials employed for switching in these three patents are disclosed therein as providing good nanosecond time interval switching. However, it has more recently been found that TCNQ or derivative localized migration or diffusion tends to occur in the region of current flow or laser beam contact upon repeated switching, thereby diminishing the useful lifespan of these devices.
At least one attempt has been made to minimize this migration or diffusion problem. Specifically, Hoshino et al, "Reversibly Write-Erase Properties of CuTCNQ Optical Recording Media", Japanese Journal of Applied Physics, Part 2, 25 (4), L341 (1986), discloses achieving about 50 write-erase cycles by applying a zinc sulfide protective layer over a CuTCNQ film prior to initiating the write-erase cycles using a semiconductor laser. This number of cycles is expected to be insufficient for most practical applications.
The rapidly evolving technology of optical data storage has the potential to retain unprecedented amounts of information at high density using optically focused beams. In a commercial setting, it would be highly desirable to provide switching media characterized by excellent physical properties and the ability to provide repeated cycles while lending itself to economical fabrication techniques. A typical application would be for random access memory storage devices. Organic materials such as TCNQ have the potential for providing these characteristics if the above-discussed migration or diffusion problem is obviated. Accordingly, the solution to this migration or diffusion problem would be highly desirable.